consul/agent/dns/dns_record_maker.go

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// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: BUSL-1.1
package dns
import (
"regexp"
"strings"
"time"
"github.com/miekg/dns"
"github.com/hashicorp/consul/agent/discovery"
)
// dnsRecordMaker creates DNS records to be used when generating
// responses to dns requests.
type dnsRecordMaker struct{}
// makeSOA returns an SOA record for the given domain and config.
func (dnsRecordMaker) makeSOA(domain string, cfg *RouterDynamicConfig) dns.RR {
return &dns.SOA{
Hdr: dns.RR_Header{
Name: domain,
Rrtype: dns.TypeSOA,
Class: dns.ClassINET,
// Has to be consistent with MinTTL to avoid invalidation
Ttl: cfg.SOAConfig.Minttl,
},
Ns: "ns." + domain,
Serial: uint32(time.Now().Unix()),
Mbox: "hostmaster." + domain,
Refresh: cfg.SOAConfig.Refresh,
Retry: cfg.SOAConfig.Retry,
Expire: cfg.SOAConfig.Expire,
Minttl: cfg.SOAConfig.Minttl,
}
}
// makeNS returns an NS record for the given domain and fqdn.
func (dnsRecordMaker) makeNS(domain, fqdn string, ttl uint32) dns.RR {
return &dns.NS{
Hdr: dns.RR_Header{
Name: domain,
Rrtype: dns.TypeNS,
Class: dns.ClassINET,
Ttl: ttl,
},
Ns: fqdn,
}
}
// makeIPBasedRecord returns an A or AAAA record for the given name and IP.
// Note: we might want to pass in the Query Name here, which is used in addr. and virtual. queries
// since there is only ever one result. Right now choosing to leave it off for simplification.
func (dnsRecordMaker) makeIPBasedRecord(name string, addr *dnsAddress, ttl uint32) dns.RR {
if addr.IsIPV4() {
// check if the query type is A for IPv4 or ANY
return &dns.A{
Hdr: dns.RR_Header{
Name: name,
Rrtype: dns.TypeA,
Class: dns.ClassINET,
Ttl: ttl,
},
A: addr.IP(),
}
}
return &dns.AAAA{
Hdr: dns.RR_Header{
Name: name,
Rrtype: dns.TypeAAAA,
Class: dns.ClassINET,
Ttl: ttl,
},
AAAA: addr.IP(),
}
}
// makeCNAME returns a CNAME record for the given name and target.
func (dnsRecordMaker) makeCNAME(name string, target string, ttl uint32) *dns.CNAME {
return &dns.CNAME{
Hdr: dns.RR_Header{
Name: name,
Rrtype: dns.TypeCNAME,
Class: dns.ClassINET,
Ttl: ttl,
},
Target: dns.Fqdn(target),
}
}
// makeSRV returns an SRV record for the given name and target.
func (dnsRecordMaker) makeSRV(name, target string, weight uint16, ttl uint32, port *discovery.Port) *dns.SRV {
return &dns.SRV{
Hdr: dns.RR_Header{
Name: name,
Rrtype: dns.TypeSRV,
Class: dns.ClassINET,
Ttl: ttl,
},
Priority: 1,
Weight: weight,
Port: uint16(port.Number),
Target: target,
}
}
// makeTXT returns a TXT record for the given name and result metadata.
func (dnsRecordMaker) makeTXT(name string, metadata map[string]string, ttl uint32) []dns.RR {
extra := make([]dns.RR, 0, len(metadata))
for key, value := range metadata {
txt := value
if !strings.HasPrefix(strings.ToLower(key), "rfc1035-") {
txt = encodeKVasRFC1464(key, value)
}
extra = append(extra, &dns.TXT{
Hdr: dns.RR_Header{
Name: name,
Rrtype: dns.TypeTXT,
Class: dns.ClassINET,
Ttl: ttl,
},
Txt: []string{txt},
})
}
return extra
}
// encodeKVasRFC1464 encodes a key-value pair according to RFC1464
func encodeKVasRFC1464(key, value string) (txt string) {
// For details on these replacements c.f. https://www.ietf.org/rfc/rfc1464.txt
key = strings.Replace(key, "`", "``", -1)
key = strings.Replace(key, "=", "`=", -1)
// Backquote the leading spaces
leadingSpacesRE := regexp.MustCompile("^ +")
numLeadingSpaces := len(leadingSpacesRE.FindString(key))
key = leadingSpacesRE.ReplaceAllString(key, strings.Repeat("` ", numLeadingSpaces))
// Backquote the trailing spaces
numTrailingSpaces := len(trailingSpacesRE.FindString(key))
key = trailingSpacesRE.ReplaceAllString(key, strings.Repeat("` ", numTrailingSpaces))
value = strings.Replace(value, "`", "``", -1)
return key + "=" + value
}